ASI Newsletter - October 2018 

Snakes and Feeding

Although most snakes feed on mice and rats, some prefer frogs, lizards, birds or a variety of other creatures. Some snakes are specialist feeders, and feed primarily on one group of prey animal. Water Snakes will feed largely on frogs and fish, while Green Mambas favour birds and arboreal rodents. Snakes have different feeding habits, some actively hunt their prey whilst others sit and ambush prey. Some use their venom to overpower prey while others constrict their prey. There are exceptions like the File snake and harmless Green Snakes (Philothamnus sp.) that do not constrict and do not have venom - they grab their prey and may swallow it while still alive. Although actively hunting prey may be more effective, snakes burn up more energy searching for prey, while the opposite is true for ambush hunters. 

Probably the most useful feature snakes have for prey detection is their tongue. The forked tongue picks up scent particles in the air and deposits them on the roof of the snake’s mouth to an organ known as the Organ of Jacobson. This organ does a chemical analysis of the surrounding environment and helps the snake detect mates, predators and prey items. Having a forked tongue allows the snake to determine which direction the scent is coming from. Snakes like Egg-eaters can smell birds’ eggs from quite a distance and use their tongue to hone in on the meal.

Young snakes are born or hatch with the instinct to hunt and venomous species are born or hatch with fully functioning fangs and venom. Often hatchling snakes will stay in the egg for a while after hatching to absorb additional yolk and nutrients. This yolk can last the young snake a couple of months until it can find its first meal.

The metabolisms of a snake is controlled by temperature and in warmer months they feed more frequently. In the cold months, snakes can become dormant and their energy requirements are minimal, meaning they don’t need to feed as often. They also cannot metabolise food if the temperature drops too low. The size of the meal also determines how regularly they need to feed. A Python eating a small antelope will take around two weeks to digest the meal and the snake won’t need to eat again for a few months. A Black Mamba eating a large rat, will have digested it within a few days and will need to eat another meal in a couple of weeks.

Rodents

Rodents form the main diet for many species, from Cobras and Adders to the harmless Brown House Snakes. Many African rodents form burrows underground and snakes utilise these burrows to hunt for them. Snakes can also take on large meals and we have seen Brown House Snakes with up to six mice in their stomachs in one go. Many farms have feed lots or grain sheds that attract rats and mice and snakes often follow them. In the Cape, the large Mole Snakes take on the ferocious giant moles of the sand dunes. Rodents often bite snakes back when being caught and a large rat can cause a lot of damage to a snake’s head whilst being bitten or constricted.

A Brown House Snake (Boaedon capensis) eating a rodent.

Small Mammals

Mammals such as hyrax, primates, small antelope and even feral cats have been recorded in the diet of some of our larger snakes. Pythons, Black Mambas and Gaboon Adders can eat large meals and large mammals fall into their diet. Southern African Pythons are well known to eat primates and mammals such as small antelope up to the size of an Impala or female Bushbuck. Gaboon Adders are also known to take large prey, and animals such as Spotted Genet, Red Duiker and even feral cats have been documented in their diet. Large Black Mambas have recently been seen around Durban eating young feral cats and in the Transkei they have also been seen eating Rock Hyrax of up to 3 kilograms.

Frogs and Toads

Many snakes are frog or toad specialists. Species like Night Adders, Rinkhals, Water Snakes (Lycodonomorphus sp.) and the Herald Snake are often found in damp areas or around vleis, dams and rivers in search of frogs and toads. Toads can often have toxins in their parotid glands on the back of the head and only some snakes can handle the toxins. Recently a snake handler fed his pet White-lipped Tree Viper from Asia one of our indigenous Red Toads and the Viper was dead in the morning. In a study by The Alexander Herp Lab at Wits University, they filmed Puff Adders in ambush positions and showed that Puff Adders actually use their tongue to attract toads into striking range. They also showed that Puff Adders were able to identify the toxic Banded Rubber Frog and would not strike at or eat them. On warm summer nights near pans and vleis, it is not uncommon to find multiple Brown Water Snakes hunting in the shallows for frogs or even climbing the reeds to try find Painted Reed Frogs. 

A Common Brown Water Snake (Lycodonomorphus rufulus) eating a Sand Frog (Tomopterna sp.)

Lizards

Another common prey group are lizards especially geckos. Snakes like the Grass or Sand Snakes (Psammophis sp.) are very efficient at catching lizards with bursts of speed. The Green Snakes like the Spotted Bush Snake are also very competent at catching lizards and geckos. Other nocturnal species such the Wolf Snakes and Spotted Rock Snakes hunt sleeping lizards in rock cracks at night. Many of the lizard specialists have large recurved teeth in order to hold onto the smooth scales of some lizards. Fossorial snakes (snakes that live underground) like the Spotted Harlequin and Purple-gloss Snakes (Amblyodipsas sp.) feed on burrowing legless lizards, occasionally seen after rains on the surface. Many of the Dwarf Adders (Bitis sp.) also ambush lizards in rocky or sandy habitats.

A Western Natal Green Snake (Philothamnus natalensis occidentalis) eating a Variable Skink (Trachylepis varia)

Birds

Birds are found in the diet of a few snakes. Arboreal (tree – living) snakes like the Boomslang and Green Mamba are well known to eat birds and fledglings. Boomslang are often seen raiding birds’ nests and can eat an entire nest of two to three young birds. Cape Cobras in the Northern Cape are well documented for raiding Sociable Weaver nests and eating the chicks. Southern Vine or Twig Snakes  are also said to eat birds, and, in the past, it was hypothesised that the red tongue was used to imitate a worm and attract birds. However, a comprehensive study showed that Twig Snakes rarely eat birds. Occasionally, generalist feeders such as Grass or Sand Snakes, Skaapstekers, and Brown House Snakes have been seen eating birds, although this is not their normal diet.

Fish

Fish eaters are a specialist group restricted to the three Water Snakes (Green Water Snake, Brown Water Snake and Dusky-bellied Water Snake). These snakes can swim underwater and often trap fish in the shallows. They eat the fish head first to avoid the sharp spines and fins. Occasionally we see images of Brown Water Snakes  stealing Gold Fish from peoples’ ponds. Smaller fish can be swallowed underwater while larger fish are brought to the edge of the water where they are constricted first.

Water snakes eating fish (Images sourced from Facebook - Predation records Reptiles and Amphibians)

Eggs

Egg eating in snakes is well known from the Egg-eaters in the genus Dasypeltis. Egg-eaters swallow the egg whole into the neck region where they use specialised vertebrates to crack the shell. They then squeeze and swallow the contents of the egg before regurgitating the compressed shell. Egg-eaters are not the only snakes that eat eggs. Large Cobras such as Snouted Cobras  and Anchieta’s Cobra  as well as Mole Snakes  and Rinkhals  have been known to eat eggs, usually swallowing them whole and having lumps in the body until the digestive enzymes break down the shell. The Shovel-snout Snakes (Prosymna sp.) are known to eat gecko eggs, also swallowing them whole. A few snakes have also been seen eating frog eggs, usually gorging themselves.

A Common Egg-eater (Dasypeltis scabra) eating a bird’s egg

Snakes

A handful of snakes such as the Common File Snakes , Vine Snakes , Purple-gloss Snakes (Amblyodipsas sp.), Stiletto Snakes (Atractaspis sp.) Cobras (Naja sp.) and even the harmless Olive Snake have been documented eating other snakes. Cobras such as the Cape Cobra and Snouted Cobra are often photographed eating Puff Adders. The Cobras seem immune to the venom of the Puff Adder. File Snakes are known to eat other snakes including young cobras, Black Mambas and Puff Adders. The Vine Snakes are well camouflaged and often ambush Grass and Sand Snakes (Psammophis sp.) as well as harmless Green Snakes (Philothamnus sp.). Many of the fossorial snakes such as the Purple-gloss Snakes , Natal Black Snakes  and Spotted Harlequin eat blind snakes such as Bibron’s Blind Snake  and Delalande’s Blind Snake.

A Bibron’s Stiletto Snake (Atractaspis  bibronii) eating a Black-headed Centipede-eater (Aparallactus capensis)

Invertebrates

There are very few species that feed on invertebrates. The two Slug-eater species (Duberria sp.) in southern Africa are known to eat both snails and slugs and are often considered the gardeners friend. Being harmless, they eat the slugs and snails whole and alive. The Centipede-eaters (Aparallactus sp.), as the name suggest, eat centipedes. The centipede is seized and chewed to work venom into it. The centipedes usually succumb to the venom rapidly, after which it is swallowed head first. Occasionally the centipedes manage to kill and eat the snake instead. According to literature, the Reticulated Centipede-eater (Aparallactus lunulatus) has been documented eating scorpions. Insects are not well documented in southern African snakes’ diet. Young Green Water Snakes  have been said to eat grasshoppers, but these reports remain anecdotal for now. In America, young Rattlesnakes have been photographed eating grasshoppers.

A Black-headed Centipede-eater (Aparallactus capensis) eating a centipede.

The specialisation and generalist diet of many snakes have made them successful in avoiding competition with other snake species. Most species that specialise are adapted to take on their prey item efficiently. For example, a Black-headed Centipede-eater (Aparallactus capensis) bite to a human has little to no effect, yet centipedes are dead within a couple of seconds after a bite. In that case, the venom has become specialised to effect centipedes and not mammals. Many of the snake-eaters such as the file snakes may have some sort of immunity to the venom of their prey. This has allowed snakes to radiate into the multiple species that eat a variety of different prey groups.

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